The present invention relates to an adhesive closure tape tab for manufacturing absorbent articles such as diapers. In particular, the invention relates to an adhesive closure tape tab that comprises an elastic laminate. The invention further relates to a prelaminated composite tape in stable roll form from which an adhesive closure tape tab can be cut. The invention further provides an absorbent article comprising the adhesive closure tape tab according to the invention.
A disposable diaper typically has a thin, flexible, stretchy, low density polyethylene backsheet film, an absorbent core on the inside of the backsheet film, and a porous top sheet overlying the core. Such a diaper is positioned at the crotch of the wearer, the two ends of the diaper extending, respectively toward the front and back. Adjacent edges of the diaper at each side are then either positioned adjacent to each other or overlapped, a strip of pressure-sensitive adhesive tape or mechanical fastener tape being adhered to the back sheet at the border adjacent each of the two edges, holding the diaper closed.
A desirable closure system which is used for disposable articles employs a mechanical fastener, comprising for example, hook and loop fastening components. Mechanical fastening systems have the advantage that they may be repeatedly used for opening and refastening the disposable article. Closure systems which contain mechanical fasteners are described in U.S. Pat. Nos. 5,019,073 and 5,176,671, in European patent applications EP 324 578, EP 563 457 and EP 563 458 and in WO 96/21413.
The exterior of disposable absorbent articles, in particular diapers, nowadays is often a non-woven to give the diaper a cloth like feel. Accordingly, desirable closure systems for use with these diapers preferably also have a non-woven backing so as to have a cloth like feel for the diaper closure system as well. Furthermore, developments have taken place to include elasticity in the closure system which increases the comfort of the wearer of the disposable absorbent article.
WO 99/48455 for example discloses an elastic tab laminate that can be adhered to the edge of an absorbent article. The elastic tab laminate is formed using a co-extruded elastic film comprising at least one elastic layer that has on one face a partially extensible non-woven layer. At the other face, there is provided a pressure sensitive adhesive layer and/or a component of a mechanical fastener system.
EP 704 196 discloses a fastening tape for a disposable diaper. The fastening tape includes a stretchable elastic material secured to one surface of the tape at least at both ends thereof thereby bridging a section of the fastening tape. The length of the fastening tape bridged by the elastic tape is longer that the elastic tape in its relaxed state.
However, the elastic tab laminate and fastening tape disclosed in these two patent applications have the disadvantage that tie skin of the wearer may be exposed to the elastic film which may cause irritation of the skin because the film may rub over the skin during repeated expansion and relaxation of the elastic film. This will in particular be the case with sensitive skins such as the skin of babies. Accordingly, it would be desirable to develop an elastic closure tape tab that would not have this disadvantage and that at the same time provides a good performance, i.e. provides good elasticity and reliable closing of the disposable absorbent article and that is compatible with existing manufacturing methods of disposable absorbent articles. Preferably, the elastic closure tape tab can be manufactured in an easy and cost effective way.
The present invention provides in one aspect, an adhesive closure tape tab that comprises an elastic laminate of an elastic film that has on at least a first major side an expandable fibrous layer of non-woven thermoplastic polymer fibers. The adhesive closure tape tab can be easily manufactured and is compatible with existing manufacturing equipment. Moreover, the adhesive closure tape tabs of the present invention are less irritating for the skin and therefore provide more comfort to the wearer of an adsorbent article having an adhesive closure tape tab according to this invention.
In a preferred embodiment, the expandable fibrous layer of the elastic laminate of the adhesive closure tape tab according to this invention is provided on both major sides of the elastic film. By the term expandable fibrous layer is meant that the fibrous layer can be expanded when the elastic film to which the fibrous layer is secured is stretched. Since the fibrous layer itself is non-elastic, the expandability of the layer is achieved by securing a fibrous layer to the elastic film such that the length of the fibrous layer is longer than the length of the elastic film in its relaxed state. Accordingly, it will be possible to expand the fibrous layer upon stretching of the elastic film until the elastic film is stretched to a length equal to the length of the fibrous layer. Stretching beyond this limit will require substantial increase in the stretch force because it would require deformation of the fibrous layer. The fibrous layer is generally coextensive with the elastic film and will preferably have an expandability of at least 30% and preferably at least 75%, that is to say that the elastic laminate can be stretched by at least 30% and preferably at least 75% of its length in the relaxed state. Typically, the expandability of the fibrous layer is between 50 and 400% and most preferably between 75% and 200%.
The fibrous layer is secured to the elastic film in intervals, i.e. when viewed in the longitudinal direction, portions of the fibrous layer that are connected to the elastic film are alternated with portions of the fibrous layer that are not connected to the elastic film layer. This may be achieved by a technique called ringrolling as disclosed in EP 704196 or alternatively, by corrugating the fibrous layer to form arcuate portions and anchor portions therein and then extruding a molten thermoplastic material thereon that forms the elastic film when cooled. This latter technique is described in detail in WO 99/48455.
The elastic film comprises a material that exhibits elastomeric properties at ambient conditions, i.e. the material will substantially resume its original shape after being stretched. Preferably, the elastomer will sustain only a small permanent set following deformation and relaxation, which set is preferably less than 30% and more preferably less than 20% of the original 50% to 500% stretch. The elastomeric material can be either pure elastomers or blends with an elastomeric phase or content that will still exhibit substantial elastomeric properties at room temperature. Suitable elastomeric thermoplastic polymers include block copolymers or the like. These block copolymers are described in for example U.S. Pat. Nos. 3,265,765; 3,562,356; 3,700,633; 4,116,917 and 4,156,673. Particularly useful are styrene/isoprene, butadiene or ethylene-butylene/styrene block copolymers. Generally, the block copolymers contain an A block and a B block. These blocks may be arranged in any order including linear, radial, branched or star block copolymers. Other useful elastomeric compositions can include elastomeric polyurethanes, ethylene copolymers such as ethylene vinyl acetates, ethylene/propylene copolymer elastomers or ethylene/propylene/diene terpolymer elastomers. Blends of these elastomers with each other or with modifying elastomers are also contemplated.
Viscosity reducing polymers and plasticizers can also be blended with the elastomers such as low molecular weight polyethylene and polypropylene polymers and copolymers, or tackifying resins such as Wingtack(trademark), aliphatic hydrocarbon tackifiers available from Goodyear Chemical Company. Examples of tackifiers include aliphatic or aromatic hydrocarbon liquid tackifiers, polyterpene resin tackifiers, and hydrogenated tackifying resins. Aliphatic hydrocarbon resins are preferred.
Additives such as dyes, pigments, antioxidants, antistatic agents, bonding aids, antiblocking agents, slip agents, heat stabilizers, photostabilizers, foaming agents, glass bubbles, reinforcing fiber, starch and metal salts for degradability or microfibers can also be blended into the elastomeric composition for making the elastic film.
In a preferred embodiment in connection with the present invention, the elastic film comprises an elastomeric core layer of elastomeric material provided on one or both major surfaces with a skin layer. Such a multilayer film can conveniently be produced through co-extrusion. The use of a skin layer is particularly useful on the side where the non-elastic adhesive tape is being attached because the skin layer may function as a barrier layer to migration of tackifiers and other low molecular weight species into the elastic core layer and also creates a more stable surface for the attachment of the non-elastic adhesive tapes, particularly when the skin layer is an inelastic material.
The skin layers can be stretched beyond an elastic limit of these skin layers. The skin layers are generally nontacky materials or blends formed of any semicrystalline or amorphous polymer(s) which are less elastomeric than the elastic core layer, generally inelastic, and which will undergo relatively more permanent deformation than the elastic core layer at the percentage that the elastic film is stretched. Elastomeric materials such as olefinic elastomers, e.g. ethylene-propylene elastomers, ethylene propylene diene polymer elastomers, metallocene polyolefin elastomers or ethylene vinyl acetate elastomers, or styrene/isoprene, butadiene or ethylene-butylene/styrene (SIS, SBS, SEBS) block copolymers, or polyurethanes or blends with these materials can be used as long as the skin layers provided are generally nontacky and preferably can act as barrier layers to any adhesive applied. Generally, the elastomeric materials used are present in a blend with nonelastomeric materials in a weight percent range of 0-70%, preferably 5-50%. High percentages of elastomer in the skin layer(s) generally require of antiblock and/or slip agents to reduce the surface tack and roll unwind force. Preferably, these skin layers are polyolefinic formed predominately of polymers such as polyethylene, polypropylene, polybutylene, polyethylene-polypropylene copolymer, however, these skin layers may also be wholly or partly polyamide, such as nylon, polyester, such as polyethylene terephthalate, or the like, and suitable blends thereof. Generally, the skin layer material following the stretching and recovery of the coextruded elastic is in contact with the elastic core layer material in at least one of three suitable modes; first, continuous contact between the elastic core layer and the microtextured skin layer; second, continuous contact between the layers with cohesive failure of the core layer material under the microtextured skin folds; and third, adhesive failure of the skin layer to the core layer under the microtextured folds with intermittent skin layer to core layer contact at the microtexture fold valleys. Generally, in the context of the present invention, all three forms of skin-to-core contact are acceptable. However, preferably the skin and core layers are in substantially continuous contact so as to minimize possibility of delamination of the skin layer(s) from the elastic core layer.
Generally, the overall elastic core layer to skin layer(s) thickness ratio of the elastic film will be at least 1.5, preferably at least 5.0 but less than 1000 and most preferably from 5.0 to 200. Generally, the overall caliper of the multilayer elastic film is preferably 25 to 200 microns. The addition of the skin layer materials generally tends to reinforce the elastic film material. However, in the present invention the skin layers are provided to be sufficiently thin and/or soft so that little or no reinforcement of the elastomeric core layer occurs and the film is elastic in its initial elongation as well as its second and subsequent elongations at suitably low stress elongation forces and low hysteresis loss levels when the elastic is cycled in use (e.g. by dimensional changes caused by breathing).
Generally, the elastic film has elastic properties on its first and preferably its subsequent elongations similar to that of the elastomeric layer material itself with no distinct yield point or range in the first elongation.
The fibrous layer of the elastic laminate is typically a nonwoven web of thermoplastic polymer fibers. Suitable processes for making, the nonwoven web include, but are not limited to, airlaying, spunbond, spunlace, bonded melt blown webs and bonded carded web formation processes. Spunbond nonwoven webs are made by extruding a molten thermoplastic as filaments from a series of fine die orifices in a spinneret. The diameter of the extruded filaments is rapidly reduced under tension by, for example, non-eductive or eductive fluid-drawing or other known spunbond mechanisms, such as described in U.S. Pat. No. 4,340,653 (Appel et al.); U.S. Pat. No. 3,692,618 (Dorschner et al.); U.S. Pat. No. 3,338,992 and U.S. Pat. No. 3,341,394 (Kinney); U.S. Pat. No. 3,276,944 (Levy); U.S. Pat. No. 3,502,538 (Peterson); U.S. Pat. No. 3,502,763 (Hartman); and U.S. Pat. No. 3,542,615 (Dobo et al.). The spunbond web is preferably bonded. The nonwoven web layer also may be made from bonded carded webs. Carded webs are made from separated staple fibers, which fibers are sent through a combing or carding unit which separates and aligns the staple fibers in the machine direction so as to form a generally machine direction-oriented fibrous nonwoven web. However, randomizers can be used to reduce this machine direction orientation. Once the carded web has been formed, it is then bonded by one or more of several bonding methods to give it suitable tensile properties. One bonding method is powder bonding wherein a powdered adhesive is distributed through the web and then activated, usually by heating the web and adhesive with hot air. Another bonding method is pattern bonding wherein heated calender rolls or ultrasonic bonding equipment are used to bond the fibers together, usually in a localized bond pattern though the web can be bonded across its entire surface if so desired. Generally, the more the fibers of a web are bonded together, the greater the nonwoven web tensile properties.
Airlaying is another process by which fibrous nonwoven webs useful in the present invention can be made. In the airlaying process, bundles of small fibers usually having lengths ranging between about 6 to about 19 millimeters are separated and entrained in an air supply and then deposited onto a forming screen, often with the assistance of a vacuum supply. The randomly deposited fibers are then bonded to one another using, for example, hot air or a spray adhesive.
Alternatively known melt blown webs or spunlace nonwoven webs or the like can be used to form the fibrous layer of the elastic laminate. Melt blown webs are formed by extrusion of thermoplastic polymers from multiple die orifices, which polymer melt streams are immediately attenuated by hot high velocity air or steam along two faces of the die immediately at the location where the polymer exits from the die orifices. The resulting fibers are entangled into a coherent web in the resulting turbulent airstream prior to collection on a collecting surface. Generally, to provide sufficient integrity and strength for the present invention, melt blown webs must be further bonded such as through air bonding, heat or ultrasonic bonding as described above.
In accordance with the present invention, a first and a second non-elastic adhesive tape are attached opposite of each other to the elastic film such that on the first major side the elastic film comprises the expandable fibrous layer and on the second major side, the first and second non-elastic adhesive tape are attached. The first and second non-elastic adhesive tape each comprise a fibrous layer and an adhesive layer. The fibrous layer of the non-elastic adhesive tapes may be prepared as describe above and is generally a dimensionally stable layer having a thickness that is typically between 10 and 150 g/m2 and preferably between 20 g/m2 and 150 g/m2. The fibrous layer of the non-elastic adhesive tapes preferably does not allow the adhesive of the adhesive layer on one side to blead through to the other side. Alternatively, if the fibrous layer would allow adhesive to blead through, a film barrier layer could be provided between the adhesive layer and the fibrous layer. Such a film barrier layer could also be provided to improve the strength of the adhesive tape if the fibrous layer in itself does not provide sufficient strength. The adhesive layer is used to secure the non-elastic adhesive tape to the elastic film. The adhesive layer can be any conventional solution or hot-melt coated adhesive such as a tackified synthetic rubber resin adhesive, an acrylate adhesive, a silicone adhesive, a polyalpha-olefin adhesive, blends and the like. The first and second non-elastic adhesive tape are each secured at one end of the elastic laminate such that a portion of each adhesive tape extends beyond the elastic film. Accordingly, the extended portion of the first or second non-elastic adhesive tape may be used to attach the adhesive closure tape tab to one edge of a disposable absorbent article such as a diaper whereas the extending portion of the other non-elastic adhesive tape will comprise the closure system.
In accordance with one embodiment in connection with the present invention, the closure system may simply consist of the extending portion of one of the non-elastic adhesive tapes. Accordingly, the adhesive layer of the non-elastic adhesive tapes will, in such a system, be used to close the absorbent article by attachment of the extending portion of that non-elastic adhesive tape to a landing zone adapted therefor on the front of the absorbent article. Alternatively, the closure system will comprise a mechanical fastener. In the latter case the extended portion of one of the first and second non elastic adhesive tape will be provided with one of the two mutually engaging means of the mechanical fastener system, typically the hook part of a hook and loop mechanical fastener system. The loop component will generally be formed by the outer surface of the absorbent article.
According to a preferred embodiment, the fibrous layer of the non-elastic adhesive tape is provided on the side opposite to the side having the adhesive layer, with a release layer. It is particularly desirable when the adhesive closure tape tabs are to be stacked on top of each other such as for example in a roll of prelaminated composite tape from which the adhesive closure tape tabs of the invention can be cut. In such a prelaminated composite tape in roll form, the first and second non-elastic adhesive tapes and the elastic film extend axially so that by cutting a piece from the roll, an adhesive closure tape tab with the desired width can be obtained (the length of the adhesive closure tape tab being determined by the width of the roll). Suitable release coatings that can be provided on the fibrous layer of the non-elastic adhesive tapes are well-known to those skilled in the art and include for example UV-curable silicone release coatings and polyurethane based silicone release coatings.
The first and second non-elastic adhesive tapes may be the same or different and may comprise further layers. For example, there may be provided a film layer between the adhesive layer and the fibrous layer of the non-elastic adhesive tapes.